Lab – The Digital Oscilloscope (Answers) Lab – The Digital Oscilloscope (Instructor Version)

Topology Lab - The Digital Oscilloscope (Answers) 2


Use Falstad’s Web Circuit Simulation Tool to get familiar with waveforms and basic electronics components.

Background / Scenario

Electronics is deeply connected to IoT. In this lab you will use Falstad’s Web Circuit Simulatior to visualize waveforms. Secondarily, you will gain a better understanding of their functions and usage by changing the arragement and values of some specifc electronic components.


Falstad’s Circuit Simulator Tool: http://www.falstad.com/circuit/

Iain Sharp’s JavaScript port of Falstad’s Circuit Simulation Tool: http://lushprojects.com/circuitjs/

Part 1: The Circuit Simulator and Basic Circuits

You will use the Web Circuit Simulator located inside the Connected Things course, page to complete this lab.

Using the Basic LED circuit, follow the steps below:

a. The electrons flow from the battery’s positive terminal to the battery’s negative terminal, passing through the resistor and the LED in the way. The flow of electrons through the LED, lights it up. Hover the mouse on the LED and write down the values you see.

b. Hover the mouse on the resistor and write the values you see.

What’s the voltage on the LED?

What’s the voltage on the resistor?

What voltage of the battery?

Red LEDs need around 2V to operate. Since the battery is 5V, the resistor is used and dimensioned to protect the LED by limiting the voltage on it. If the resistor wasn’t used, the LED could be permanently damaged.

Part 2: Visualizing Signals

While electrical signals are not visible, specific equipment can be used to measure and display such signals. Known as waveforms, common signal shapes have special names. When the signal amplitude (maximum and minimum levels) conforms to a mathematical sine function, the wave is said to be a sine wave.

a. Using Falstad’s Web Circuit Simulator, navigate to Circuits >> Basic >> LRC Circuit.

b. While the details of this circuit is out of the scope of this course, notice how it creates sine waves on the bottom portion of the screen. The circuit design forces the electrons to change their flow direction, creating alternating signal levels. A sine wave is created.

Note: Alternating Current (AC) is used by many countries to transport energy through long physical distances. Because the polarity varies over with AC, the electrons are also forced to change flow direction and therefore, AC also generates sine waves.

Square waves are most seen in digital circuits. Since digital circuits often deal with discrete amplitudes, representing 0s and 1s for example, the wave form becomes very distinct.

c. Using Falstad’s Web Circuit Simulator, navigate to Circuits >> 555 Timer Chip >> Square Wave Generator.

d. The details of this circuit are also out of the scope of this course but notice how it creates square waves on the bottom right portion of the screen.

Challenge question: Alternating Current (AC) creates square waves or sine waves? Explain.
Sine waves, because the polarity varies over with AC, the electrons are also forced to change flow direction and therefore. AC also generates sine waves.

Part 3: The Oscilloscope

Falstad’s Web Circuit Simulator allows for signal visualization but in the real world, equipment is required when visualizing electrical signals. Known as an oscilloscope, this piece of equipment is a powerful troubleshooting tool when working with circuits and signals. Many models and brands of oscilloscope are available, varying in price and functionality.

a. Take some time and look at different circuits in the Falstad’s Web Circuit Simulator. The waveforms most of the circuits display will give you a better understanding of what is happening in the circuits.

b. Take some time and search the oscilloscope pictures. This will give you a better understanding of the waveforms they can display.

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